Bug 15992

Summary:	Unexpected behaviour with TOOLCHAIN
Product:	[Build System, Metadata & Runtime] OE-Core	Reporter:	Ross Burton <ross.burton>
Component:	devtools / tool chain	Assignee:	Ross Burton <ross.burton>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	Medium+	CC:	antonin.godard, meta.mr.watcher, meta.watcher, raj.khem, randy.macleod
Version:	5.2
Target Milestone:	5.3 M4
Hardware:	x86
OS:	Multiple
Whiteboard:
OS type for building Yocto:	---	Type of Regression:	---
Verified:		Documentation change:	Yes (doc changes required)

Description Ross Burton 2025-10-09 17:04:04 UTC

If I set TOOLCHAIN=clang in local.conf and then build a native recipe, the overrides that are used as not quite as expected:

$ bitbake-getvar -r gn-native --value OVERRIDES
linux:aarch64:pn-gn-native:layer-core::poky:class-native:toolchain-clang:forcevariable

Specifically, "toolchain-clang" is unexpected because the build will be using the host GCC.

I suspect the answer is "set PREFERRED_TOOLCHAIN instead", which is fine. But should native.bbclass be setting TOOLCHAIN=TOOLCHAIN_NATIVE too?

Comment 1 Khem Raj 2025-10-09 20:23:10 UTC

(In reply to Ross Burton from comment #0)
> If I set TOOLCHAIN=clang in local.conf and then build a native recipe, the
> overrides that are used as not quite as expected:
> 
> $ bitbake-getvar -r gn-native --value OVERRIDES
> linux:aarch64:pn-gn-native:layer-core::poky:class-native:toolchain-clang:
> forcevariable
> 
> Specifically, "toolchain-clang" is unexpected because the build will be
> using the host GCC.
>

PREFERRED_TOOLCHAIN_{TARGET|NATIVE|SDK} are new interfaces
 
> I suspect the answer is "set PREFERRED_TOOLCHAIN instead", which is fine.
> But should native.bbclass be setting TOOLCHAIN=TOOLCHAIN_NATIVE too?

yeah perhaps might be ok, I also wonder if we have similar issue with SDK case.

Comment 2 Ross Burton 2025-10-16 14:39:37 UTC

We should at least have something in the migration guide about this. We should say that clang has been integrated into core, meta-clang is no longer essential, but when picking a compiler at a distro level PREFERRED_TOOLCHAIN should be used instead of TOOLCHAIN.

Antonin, can you add something like that?

Comment 3 Antonin Godard 2025-10-16 15:18:05 UTC

I added a note on that to the release note updates I sent today:

>     .. warning::
>        The :term:`TOOLCHAIN` should **not** be set globally. For overridding
>        the toolchain globally, use :term:`PREFERRED_TOOLCHAIN_TARGET`,
>        :term:`PREFERRED_TOOLCHAIN_NATIVE` and :term:`PREFERRED_TOOLCHAIN_SDK`.

(I realize now I'm missing "variable" after TOOLCHAIN, will fix that)

https://lore.kernel.org/yocto-docs/20251016-release-note-5-3-second-hunk-v1-17-20f21db1f93c@bootlin.com/

Do you think that's enough or should I mention something else?

Comment 4 Ross Burton 2026-03-12 15:14:14 UTC

The doc changes look good.